ARP Pro/High Performance Bolt Differences?

[cv2065]

Anyone know why one would use the Pro Series ARP bolts vs. the High Performance ones? For example, the ARP High Performance flywheel bolts are rated at 180,000 PSI, and install with Ultra Lube under the head, Loctite on the threads and 75 ft/lbs of torque. The ARP Pro flywheel bolts are rated at 200,000 PSI, and install with Ultra Lube under the head, Loctite on the threads and 85 ft/lbs of torque.

Why would one need one over the other? ARP doesn't say a whole lot about it on their website, other than one is stronger than the other.

[progmgr1]

Idle speculation from a retired mechanical engineer: The different bolt ratings are probably related to the differing tensile strength of the two different steel alloys used. Higher tensile strength = can be tightened using more torque = higher clamping force (preload). Also, shear strength (ability to resist lateral forces) (think how hard is it to cut paper vs. sheet aluminum using scissors / shears) is proportional to tensile strength. So, the higher rated bolts are slightly harder to slice through if preload is lost and the joint slips.

What all this means is that the Pro series bolts clamp the flywheel down 10-15% harder than the High Performance series bolts.

The loads on the flywheel bolts come from the engine on one side and the wheels / tires / transmission / clutch on the other. So, my guess is that you would use the Pro series bolts if you have a boosted, high-torque engine and big meaty racing slicks in the back and you are drag racing (dumping the clutch at high engine RPM magnifies the loads on the joint.) The High Performance series should be fine if you are doing Auto-X or road racing, where the shifts are usually smoother = less load on the joint.

HTH Keith HR #894

[cv2065]

The loads on the flywheel bolts come from the engine on one side and the wheels / tires / transmission / clutch on the other. So, my guess is that you would use the Pro series bolts if you have a boosted, high-torque engine and big meaty racing slicks in the back and you are drag racing (dumping the clutch at high engine RPM magnifies the loads on the joint.) The High Performance series should be fine if you are doing Auto-X or road racing, where the shifts are usually smoother = less load on the joint.

HTH Keith HR #894

Great explanation Keith. Thanks! I've read that it also depends on the material you are putting the bolts into. I'm not sure what the tensile strength of the 7/16-20 threads would be in say a cast or forged crank, at a recommended 85 ft/lbs for the Pro bolts with lube.

[Dgc333]

Most all OE fasteners used in high stress applications are SAE Grade 8 which has a tensile strength of 130,000 psi. Unless you are planning on subjecting your threaded fasteners to a much higher load (such as boost) either of those ARP fasteners are over kill.

FWIW, many years ago I was building and engine and decided to go with ARP fasteners for the main caps because I had plans to make a lot more power than stock. The interesting tid bit was the ARP instructions gave a torque specification for when you used their moli lube and a much higher torque if you were using the FSM recommended motor oil. As I recall the difference was like 75 ft-lbs to 115 ft-lbs. Presumably the different torques resulted in the same clamping force.

[progmgr1]

Yep, you nailed it. The better lube reduces the friction between the bolt head and the mating surface, and between the bolt threads and the receiving threads. That way more of the applied torque goes into stretching the bolt = clamping force. IIRC, there is a blog entry on the ARP website about reducing the tightening torque for well-lubricated threads.

And I agree that either of the ARP bolts would be overkill for a non-drag racing engine build.

Keith HR #894

[Skuzzy]

I have always used ARP fasteners in my engine builds. Not so much for the strength, but those cold rolled threads just make it nice to work with. Easier to get accurate torque readings as well versus cut threads.

[cv2065]

I have always used ARP fasteners in my engine builds. Not so much for the strength, but those cold rolled threads just make it nice to work with. Easier to get accurate torque readings as well versus cut threads.

I agree Skizzy. The fit and finish on the ARP bolts are amazing. Fun fact after speaking to them. They discontinued the high performance line with the 180K PSI and will now just have the Pro performance bolts. Guess they figured out they were too close as well.